The demonstrators accuse the government of cracking down on protesters who helped topple the government of former president Gotabaya Rajapaksa last month.
Police fired tear and water cannons at students gathered opposite the Elphinstone Theatre in Maradana, Colombo on Tuesday evening to protest against the arrests made via the Prevention of Terrorism Act.
25 people were later arrested for taking part in the protest.
Earlier this month, Human Rights Watch had said the Sri Lankan government was "using emergency regulations to harass and arbitrarily detain activists seeking political reform and accountability for the country’s economic crisis".
Sri Lankan lawmakers voted in acting President Ranil Wickremesinghe as the new president last month, hoping his long experience in government could help pull the country out of a crippling economic and political crisis.
The six-time prime minister won 134 votes in the 225-member parliament, despite public anger with the ruling elite after months of severe shortages of fuel, food, and medicines.
Many of the hundreds of thousands who poured into the streets in July to force the ouster of Rajapaksa had wanted Wickremesinghe gone too, labeling him an ally of the Rajapaksa family.
Wickremesinghe has denied being close to the Rajapaksa clan.
Protesters stormed Wickremesinghe`s official residence last month when he was prime minister and burnt down his private house.
